Can a commerce graduate start a career in IT with software testing if yes then how?

Yes you definitely do !! I know many commerce grads who have ended up in IT, and in many ways you might have a slight edge over the "classical engineers" as most of the software is written for the financial domain and you have some background in it. How you can go about doing it, get a MCA/equivalent degree if possible, DOEACC degrees are a possibility. Whether or not you get a formal degree you need to self learn, software is one field where skills matter more than degrees, build apps, test for open source projects and so on, once you break through and have a couple of years of experience no one care about your academic degrees If you think you will enjoy it, you can go for it ... your degree won't stop you :)